The present invention relates generally to the processing of electronic images for video display, more particularly to the processing of computer-generated video images, and especially to the manipulation of complex video images involving the presentation of overlay images over a background image.
The use of computers to generate video images has become widespread and has brought with it the need to efficiently generate and manipulate such images. When such images involve the use of the technique of overlay, in which a background image is displayed with one or more secondary images overlaying various parts of the background image, the operator needs to be provided with several convenient and efficient controls so that the final display image can be produced in the minimum time.
The colors used in displaying the overlay images must be readily changeable as needed to enhance the appearance of the overlay images with respect to the background image. The position of the overlay images must also be easily altered by the operator. Further, it must be possible to provide some degree of protection to the various image portions such that an overlay image can be prevented from obscuring significant details of the image(s) lying beneath it.
Computer systems for handling these matters have in the past relied to a significant extent on construction of a complex display image including overlays by the use of a single image plane representing the complex display image in memory. In order to alter the various portions of the image to insert overlays, the host computer utilized software to serially read each of the data points in the region of the memory plane where changes were to be made, and then wrote new data in this region to represent the altered image.
Such software-intensive techniques were slow and cumbersome, and provided no backup capability, since the original data values in the image memory plane were lost as soon as new data was written into the affected addresses.